The Russo-American War, also known as the Invasion of America or the Second Great Patriotic War by Russia, was a large conflict fought on a scale not seen since World War II. The initial invasion was the largest in military history, with almost four million Russian (and other allied) troops taking part, against some initial troop numbers with less than three million American defenders. Ultimately, Russia, collaborators, and allies fielded some nearly nine million combatants, while the American government and independent groups responded with around eleven million troops. The conflict raged on for five years, from 2019 to 2026, and resulted in more than seventy million casualties overall, being the deadliest conflict in history, surpassing World War II.

The invasion began in 2019, with the Russian military and a few allied units striking key cities on the east and west coasts of the United States. This resulted in the battles of New York, Boston, Seattle, Los Angeles, and several others. It saw initial Russian success, with the cities being taken and much land being secured around them. Additional ground forces were then moved in by Russia and allies. By early 2020, offensives were in full operation, going on on the east and west coasts against the shocked and demoralized defenders. Foreign volunteers aided the US forces, and meanwhile American collaborators fought alongside Russia. By 2023, most of the coastal states were taken and Russian forces pushed further inland.

By 2024, much of the Midwest fell to allied troops, with US loyalists holding out in the central states of the country. They held out and slowed the allied advance. For several months it was a statement, until India offered to bring in additional troops, turning the tide in the allies' favor. The US attempted one offensive during this time, but it failed and caused heavy losses. The US navy particularly was heavily hit, many of its vessels were captured as the coasts were taken.